Rendering and Compositing - Blender Master Class: A Hands-on Guide to Modeling, Sculpting, Materials, and Rendering - page 236

Extra Ambient Occlusion
Next, I used a Mix node ( shift -A 4 Color 4 Mix) to
increase the strength of the ambient occlusion effect
on the body render layer. I set the Blend mode of
the Mix node to Multiply and used the Image output
of the body render layer as the first input. I used
the ambient occlusion pass (from the socket labeled
AO) as the second input.
To increase the effect, I darkened the ambient
occlusion pass with a Curves node before multiply-
ing it with the image. To do so, I added an RGB
Curves node and inserted it between the ambient
occlusion output of the Render Layer node and the
Multiply node. To do this quickly, drag the node
over the connection between two other nodes (you
should see the connection highlight) and release it
to insert it in a chain between the other two nodes.

Finally, I made the curve on the RGB Curves
node a bit steeper (see Figure 14-6).

Combining the Body and Fur
Next, I added an Alpha Over node ( shift -A 4 Color 4
Alpha Over), connecting the body as the first input
and the fur as the second. To get the correct results
when compositing layers with straight alpha, which
I selected when choosing the Render settings ear-
lier (see “Render Layers” on page 234), I enabled
Convert Premultiply for this node. This should pro-
duce the expected result without any dark fringing.
To place the Bat Creature on a dark gray back-
ground, I used a second Alpha node with an RGB
node as the first input (set to gray) and my newly
merged body and hair layers as the second input,
as shown in Figure 14-6.

Figure 14-6: Adding extra ambient occlusion to the body render layer with a Multiply node. The hair is then merged over the
top, and the composite is placed over a gray background using an Alpha Over node.